bind/genjava.go - mobile - Git at Google

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package bind

 import (
 	"bytes"
 	"fmt"
 	"go/token"
 	"io"
 	"regexp"
 	"unicode"
 	"unicode/utf8"

 	"golang.org/x/tools/go/types"
 )

 // TODO(crawshaw): disallow basic android java type names in exported symbols.
 // TODO(crawshaw): generate all relevant "implements" relationships for interfaces.
 // TODO(crawshaw): consider introducing Java functions for casting to and from interfaces at runtime.

 type ErrorList []error

 func (list ErrorList) Error() string {
 	buf := new(bytes.Buffer)
 	for i, err := range list {
 		if i > 0 {
 			buf.WriteRune('\n')
 		}
 		io.WriteString(buf, err.Error())
 	}
 	return buf.String()
 }

 type javaGen struct {
 	*printer
 	fset *token.FileSet
 	pkg  *types.Package
 	err  ErrorList
 }

 func (g *javaGen) genStruct(obj *types.TypeName, T *types.Struct) {
 	fields := exportedFields(T)
 	methods := exportedMethodSet(types.NewPointer(obj.Type()))

 	g.Printf("public static final class %s implements go.Seq.Object {\n", obj.Name())
 	g.Indent()
 	g.Printf("private static final String DESCRIPTOR = \"go.%s.%s\";\n", g.pkg.Name(), obj.Name())
 	for i, f := range fields {
 		g.Printf("private static final int FIELD_%s_GET = 0x%x0f;\n", f.Name(), i)
 		g.Printf("private static final int FIELD_%s_SET = 0x%x1f;\n", f.Name(), i)
 	}
 	for i, m := range methods {
 		g.Printf("private static final int CALL_%s = 0x%x0c;\n", m.Name(), i)
 	}
 	g.Printf("\n")

 	g.Printf("private go.Seq.Ref ref;\n\n")

 	n := obj.Name()
 	g.Printf("private %s(go.Seq.Ref ref) { this.ref = ref; }\n\n", n)
 	g.Printf(`public go.Seq.Ref ref() { return ref; }

 public void call(int code, go.Seq in, go.Seq out) {
     throw new RuntimeException("internal error: cycle: cannot call concrete proxy");
 }

 `)

 	for _, f := range fields {
 		g.Printf("public %s get%s() {\n", g.javaType(f.Type()), f.Name())
 		g.Indent()
 		g.Printf("Seq in = new Seq();\n")
 		g.Printf("Seq out = new Seq();\n")
 		g.Printf("in.writeRef(ref);\n")
 		g.Printf("Seq.send(DESCRIPTOR, FIELD_%s_GET, in, out);\n", f.Name())
 		if seqType(f.Type()) == "Ref" {
 			g.Printf("return new %s(out.read%s);\n", g.javaType(f.Type()), seqRead(f.Type()))
 		} else {
 			g.Printf("return out.read%s;\n", seqRead(f.Type()))
 		}
 		g.Outdent()
 		g.Printf("}\n\n")

 		g.Printf("public void set%s(%s v) {\n", f.Name(), g.javaType(f.Type()))
 		g.Indent()
 		g.Printf("Seq in = new Seq();\n")
 		g.Printf("Seq out = new Seq();\n")
 		g.Printf("in.writeRef(ref);\n")
 		g.Printf("in.write%s;\n", seqWrite(f.Type(), "v"))
 		g.Printf("Seq.send(DESCRIPTOR, FIELD_%s_SET, in, out);\n", f.Name())
 		g.Outdent()
 		g.Printf("}\n\n")
 	}

 	for _, m := range methods {
 		g.genFunc(m, true)
 	}

 	g.Printf("@Override public boolean equals(Object o) {\n")
 	g.Indent()
 	g.Printf("if (o == null || !(o instanceof %s)) {\n    return false;\n}\n", n)
 	g.Printf("%s that = (%s)o;\n", n, n)
 	for _, f := range fields {
 		nf := f.Name()
 		g.Printf("%s this%s = get%s();\n", g.javaType(f.Type()), nf, nf)
 		g.Printf("%s that%s = that.get%s();\n", g.javaType(f.Type()), nf, nf)
 		if isJavaPrimitive(f.Type()) {
 			g.Printf("if (this%s != that%s) {\n    return false;\n}\n", nf, nf)
 		} else {
 			g.Printf("if (this%s == null) {\n", nf)
 			g.Indent()
 			g.Printf("if (that%s != null) {\n    return false;\n}\n", nf)
 			g.Outdent()
 			g.Printf("} else if (!this%s.equals(that%s)) {\n    return false;\n}\n", nf, nf)
 		}
 	}
 	g.Printf("return true;\n")
 	g.Outdent()
 	g.Printf("}\n\n")

 	g.Printf("@Override public int hashCode() {\n")
 	g.Printf("    return java.util.Arrays.hashCode(new Object[] {")
 	for i, f := range fields {
 		if i > 0 {
 			g.Printf(", ")
 		}
 		g.Printf("get%s()", f.Name())
 	}
 	g.Printf("});\n")
 	g.Printf("}\n\n")

 	// TODO(crawshaw): use String() string if it is defined.
 	g.Printf("@Override public String toString() {\n")
 	g.Indent()
 	g.Printf("StringBuilder b = new StringBuilder();\n")
 	g.Printf(`b.append("%s").append("{");`, obj.Name())
 	g.Printf("\n")
 	for _, f := range fields {
 		n := f.Name()
 		g.Printf(`b.append("%s:").append(get%s()).append(",");`, n, n)
 		g.Printf("\n")
 	}
 	g.Printf(`return b.append("}").toString();`)
 	g.Printf("\n")
 	g.Outdent()
 	g.Printf("}\n\n")

 	g.Outdent()
 	g.Printf("}\n\n")
 }

 func (g *javaGen) genInterfaceStub(o *types.TypeName, m *types.Interface) {
 	g.Printf("public static abstract class Stub implements %s {\n", o.Name())
 	g.Indent()

 	g.Printf("static final String DESCRIPTOR = \"go.%s.%s\";\n\n", g.pkg.Name(), o.Name())
 	g.Printf("private final go.Seq.Ref ref;\n")
 	g.Printf("public Stub() {\n    ref = go.Seq.createRef(this);\n}\n\n")
 	g.Printf("public go.Seq.Ref ref() { return ref; }\n\n")

 	g.Printf("public void call(int code, go.Seq in, go.Seq out) {\n")
 	g.Indent()
 	g.Printf("switch (code) {\n")

 	for i := 0; i < m.NumMethods(); i++ {
 		f := m.Method(i)
 		g.Printf("case Proxy.CALL_%s: {\n", f.Name())
 		g.Indent()

 		sig := f.Type().(*types.Signature)
 		params := sig.Params()
 		for i := 0; i < params.Len(); i++ {
 			p := sig.Params().At(i)
 			jt := g.javaType(p.Type())
 			g.Printf("%s param_%s;\n", jt, paramName(params, i))
 			g.genRead("param_"+paramName(params, i), "in", p.Type())
 		}

 		res := sig.Results()
 		var returnsError bool
 		var numRes = res.Len()
 		if (res.Len() == 1 && isErrorType(res.At(0).Type())) ||
 			(res.Len() == 2 && isErrorType(res.At(1).Type())) {
 			numRes -= 1
 			returnsError = true
 		}

 		if returnsError {
 			g.Printf("try {\n")
 			g.Indent()
 		}

 		if numRes > 0 {
 			g.Printf("%s result = ", g.javaType(res.At(0).Type()))
 		}

 		g.Printf("this.%s(", f.Name())
 		for i := 0; i < params.Len(); i++ {
 			if i > 0 {
 				g.Printf(", ")
 			}
 			g.Printf("param_%s", paramName(params, i))
 		}
 		g.Printf(");\n")

 		if numRes > 0 {
 			g.Printf("out.write%s;\n", seqWrite(res.At(0).Type(), "result"))
 		}
 		if returnsError {
 			g.Printf("out.writeString(null);\n")
 			g.Outdent()
 			g.Printf("} catch (Exception e) {\n")
 			g.Indent()
 			if numRes > 0 {
 				resTyp := res.At(0).Type()
 				g.Printf("%s result = %s;\n", g.javaType(resTyp), g.javaTypeDefault(resTyp))
 				g.Printf("out.write%s;\n", seqWrite(resTyp, "result"))
 			}
 			g.Printf("out.writeString(e.getMessage());\n")
 			g.Outdent()
 			g.Printf("}\n")
 		}
 		g.Printf("return;\n")
 		g.Outdent()
 		g.Printf("}\n")
 	}

 	g.Printf("default:\n    throw new RuntimeException(\"unknown code: \"+ code);\n")
 	g.Printf("}\n")
 	g.Outdent()
 	g.Printf("}\n")

 	g.Outdent()
 	g.Printf("}\n\n")
 }

 const javaProxyPreamble = `static final class Proxy implements %s {
     static final String DESCRIPTOR = Stub.DESCRIPTOR;

     private go.Seq.Ref ref;

     Proxy(go.Seq.Ref ref) { this.ref = ref; }

     public go.Seq.Ref ref() { return ref; }

     public void call(int code, go.Seq in, go.Seq out) {
         throw new RuntimeException("cycle: cannot call proxy");
     }

 `

 func (g *javaGen) genInterface(o *types.TypeName) {
 	iface := o.Type().(*types.Named).Underlying().(*types.Interface)

 	g.Printf("public interface %s extends go.Seq.Object {\n", o.Name())
 	g.Indent()

 	methodSigErr := false
 	for i := 0; i < iface.NumMethods(); i++ {
 		if err := g.funcSignature(iface.Method(i), false); err != nil {
 			methodSigErr = true
 			g.errorf("%v", err)
 		}
 		g.Printf(";\n\n")
 	}
 	if methodSigErr {
 		return // skip stub generation, more of the same errors
 	}

 	g.genInterfaceStub(o, iface)

 	g.Printf(javaProxyPreamble, o.Name())
 	g.Indent()

 	for i := 0; i < iface.NumMethods(); i++ {
 		g.genFunc(iface.Method(i), true)
 	}
 	for i := 0; i < iface.NumMethods(); i++ {
 		g.Printf("static final int CALL_%s = 0x%x0a;\n", iface.Method(i).Name(), i+1)
 	}

 	g.Outdent()
 	g.Printf("}\n")

 	g.Outdent()
 	g.Printf("}\n\n")
 }

 func isErrorType(T types.Type) bool {
 	return T == types.Universe.Lookup("error").Type()
 }

 func isJavaPrimitive(T types.Type) bool {
 	b, ok := T.(*types.Basic)
 	if !ok {
 		return false
 	}
 	switch b.Kind() {
 	case types.Bool, types.Uint8, types.Float32, types.Float64,
 		types.Int, types.Int8, types.Int16, types.Int32, types.Int64:
 		return true
 	}
 	return false
 }

 // javaType returns a string that can be used as a Java type.
 func (g *javaGen) javaType(T types.Type) string {
 	switch T := T.(type) {
 	case *types.Basic:
 		switch T.Kind() {
 		case types.Bool:
 			return "boolean"
 		case types.Int:
 			return "long"
 		case types.Int8:
 			return "byte"
 		case types.Int16:
 			return "short"
 		case types.Int32:
 			return "int"
 		case types.Int64:
 			return "long"
 		case types.Uint8:
 			// TODO(crawshaw): Java bytes are signed, so this is
 			// questionable, but vital.
 			return "byte"
 		// TODO(crawshaw): case types.Uint, types.Uint16, types.Uint32, types.Uint64:
 		case types.Float32:
 			return "float"
 		case types.Float64:
 			return "double"
 		case types.String:
 			return "String"
 		default:
 			g.errorf("unsupported return type: %s", T)
 			return "TODO"
 		}
 	case *types.Slice:
 		elem := g.javaType(T.Elem())
 		return elem + "[]"

 	case *types.Pointer:
 		if _, ok := T.Elem().(*types.Named); ok {
 			return g.javaType(T.Elem())
 		}
 		panic(fmt.Sprintf("unsupporter pointer to type: %s", T))
 	case *types.Named:
 		n := T.Obj()
 		if n.Pkg() != g.pkg {
 			panic(fmt.Sprintf("type %s is in package %s, must be defined in package %s", n.Name(), n.Pkg().Name(), g.pkg.Name()))
 		}
 		// TODO(crawshaw): more checking here
 		return n.Name()
 	default:
 		g.errorf("unsupported javaType: %#+v, %s\n", T, T)
 		return "TODO"
 	}
 }

 // javaTypeDefault returns a string that represents the default value of the mapped java type.
 // TODO(hyangah): Combine javaType and javaTypeDefault?
 func (g *javaGen) javaTypeDefault(T types.Type) string {
 	switch T := T.(type) {
 	case *types.Basic:
 		switch T.Kind() {
 		case types.Bool:
 			return "false"
 		case types.Int, types.Int8, types.Int16, types.Int32,
 			types.Int64, types.Uint8, types.Float32, types.Float64:
 			return "0"
 		case types.String:
 			return "null"
 		default:
 			g.errorf("unsupported return type: %s", T)
 			return "TODO"
 		}
 	case *types.Slice, *types.Pointer, *types.Named:
 		return "null"

 	default:
 		g.errorf("unsupported javaType: %#+v, %s\n", T, T)
 		return "TODO"
 	}
 }

 var paramRE = regexp.MustCompile(`^p[0-9]*$`)

 // paramName replaces incompatible name with a p0-pN name.
 // Missing names, or existing names of the form p[0-9] are incompatible.
 // TODO(crawshaw): Replace invalid unicode names.
 func paramName(params *types.Tuple, pos int) string {
 	name := params.At(pos).Name()
 	if name == "" || name == "_" || paramRE.MatchString(name) {
 		name = fmt.Sprintf("p%d", pos)
 	}
 	return name
 }

 func (g *javaGen) funcSignature(o *types.Func, static bool) error {
 	sig := o.Type().(*types.Signature)
 	res := sig.Results()

 	var returnsError bool
 	var ret string
 	switch res.Len() {
 	case 2:
 		if !isErrorType(res.At(1).Type()) {
 			return fmt.Errorf("second result value must be of type error: %s", o)
 		}
 		returnsError = true
 		ret = g.javaType(res.At(0).Type())
 	case 1:
 		if isErrorType(res.At(0).Type()) {
 			returnsError = true
 			ret = "void"
 		} else {
 			ret = g.javaType(res.At(0).Type())
 		}
 	case 0:
 		ret = "void"
 	default:
 		return fmt.Errorf("too many result values: %s", o)
 	}

 	g.Printf("public ")
 	if static {
 		g.Printf("static ")
 	}
 	g.Printf("%s %s(", ret, o.Name())
 	params := sig.Params()
 	for i := 0; i < params.Len(); i++ {
 		if i > 0 {
 			g.Printf(", ")
 		}
 		v := sig.Params().At(i)
 		name := paramName(params, i)
 		jt := g.javaType(v.Type())
 		g.Printf("%s %s", jt, name)
 	}
 	g.Printf(")")
 	if returnsError {
 		g.Printf(" throws Exception")
 	}
 	return nil
 }

 func (g *javaGen) genFunc(o *types.Func, method bool) {
 	if err := g.funcSignature(o, !method); err != nil {
 		g.errorf("%v", err)
 		return
 	}
 	sig := o.Type().(*types.Signature)
 	res := sig.Results()

 	g.Printf(" {\n")
 	g.Indent()
 	g.Printf("go.Seq _in = new go.Seq();\n")
 	g.Printf("go.Seq _out = new go.Seq();\n")

 	returnsError := false
 	var resultType types.Type
 	if res.Len() > 0 {
 		if !isErrorType(res.At(0).Type()) {
 			resultType = res.At(0).Type()
 		}
 		if res.Len() > 1 || isErrorType(res.At(0).Type()) {
 			returnsError = true
 		}
 	}
 	if resultType != nil {
 		t := g.javaType(resultType)
 		g.Printf("%s _result;\n", t)
 	}

 	if method {
 		g.Printf("_in.writeRef(ref);\n")
 	}
 	params := sig.Params()
 	for i := 0; i < params.Len(); i++ {
 		p := params.At(i)
 		g.Printf("_in.write%s;\n", seqWrite(p.Type(), paramName(params, i)))
 	}
 	g.Printf("Seq.send(DESCRIPTOR, CALL_%s, _in, _out);\n", o.Name())
 	if resultType != nil {
 		g.genRead("_result", "_out", resultType)
 	}
 	if returnsError {
 		g.Printf(`String _err = _out.readString();
 if (_err != null) {
     throw new Exception(_err);
 }
 `)
 	}
 	if resultType != nil {
 		g.Printf("return _result;\n")
 	}
 	g.Outdent()
 	g.Printf("}\n\n")
 }

 func (g *javaGen) genRead(resName, seqName string, T types.Type) {
 	switch T := T.(type) {
 	case *types.Pointer:
 		// TODO(crawshaw): test *int
 		// TODO(crawshaw): test **Generator
 		switch T := T.Elem().(type) {
 		case *types.Named:
 			o := T.Obj()
 			if o.Pkg() != g.pkg {
 				g.errorf("type %s not defined in package %s", T, g.pkg)
 				return
 			}
 			g.Printf("%s = new %s(%s.readRef());\n", resName, o.Name(), seqName)
 		default:
 			g.errorf("unsupported type %s", T)
 		}
 	case *types.Named:
 		switch T.Underlying().(type) {
 		case *types.Interface, *types.Pointer:
 			o := T.Obj()
 			if o.Pkg() != g.pkg {
 				g.errorf("type %s not defined in package %s", T, g.pkg)
 				return
 			}
 			g.Printf("%s = new %s.Proxy(%s.readRef());\n", resName, o.Name(), seqName)
 		default:
 			g.errorf("unsupported, direct named type %s", T)
 		}
 	default:
 		g.Printf("%s = %s.read%s();\n", resName, seqName, seqType(T))
 	}
 }

 func (g *javaGen) errorf(format string, args ...interface{}) {
 	g.err = append(g.err, fmt.Errorf(format, args...))
 }

 const javaPreamble = `// Java Package %s is a proxy for talking to a Go program.
 //   gobind -lang=java %s
 //
 // File is generated by gobind. Do not edit.
 package go.%s;

 import go.Seq;

 `

 func (g *javaGen) gen() error {
 	g.Printf(javaPreamble, g.pkg.Name(), g.pkg.Path(), g.pkg.Name())

 	firstRune, size := utf8.DecodeRuneInString(g.pkg.Name())
 	className := string(unicode.ToUpper(firstRune)) + g.pkg.Name()[size:]

 	g.Printf("public abstract class %s {\n", className)
 	g.Indent()
 	g.Printf("private %s() {} // uninstantiable\n\n", className)
 	scope := g.pkg.Scope()
 	names := scope.Names()
 	var funcs []string
 	for _, name := range names {
 		obj := scope.Lookup(name)
 		if !obj.Exported() {
 			continue
 		}

 		switch o := obj.(type) {
 		// TODO(crawshaw): case *types.Const:
 		// TODO(crawshaw): case *types.Var:
 		case *types.Func:
 			g.genFunc(o, false)
 			funcs = append(funcs, o.Name())
 		case *types.TypeName:
 			named := o.Type().(*types.Named)
 			switch t := named.Underlying().(type) {
 			case *types.Struct:
 				g.genStruct(o, t)
 			case *types.Interface:
 				g.genInterface(o)
 			default:
 				g.errorf("%s: cannot generate binding for %s: %T", g.fset.Position(o.Pos()), o.Name(), t)
 				continue
 			}
 		default:
 			g.errorf("unsupported exported type: ", obj)
 		}
 	}

 	for i, name := range funcs {
 		g.Printf("private static final int CALL_%s = %d;\n", name, i+1)
 	}

 	g.Printf("private static final String DESCRIPTOR = %q;\n", g.pkg.Name())
 	g.Outdent()
 	g.Printf("}\n")

 	if len(g.err) > 0 {
 		return g.err
 	}
 	return nil
 }
	// Copyright 2014 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package bind

	import (
	"bytes"
	"fmt"
	"go/token"
	"io"
	"regexp"
	"unicode"
	"unicode/utf8"

	"golang.org/x/tools/go/types"
	)

	// TODO(crawshaw): disallow basic android java type names in exported symbols.
	// TODO(crawshaw): generate all relevant "implements" relationships for interfaces.
	// TODO(crawshaw): consider introducing Java functions for casting to and from interfaces at runtime.

	type ErrorList []error

	func (list ErrorList) Error() string {
	buf := new(bytes.Buffer)
	for i, err := range list {
	if i > 0 {
	buf.WriteRune('\n')
	}
	io.WriteString(buf, err.Error())
	}
	return buf.String()
	}

	type javaGen struct {
	*printer
	fset *token.FileSet
	pkg *types.Package
	err ErrorList
	}

	func (g javaGen) genStruct(obj types.TypeName, T *types.Struct) {
	fields := exportedFields(T)
	methods := exportedMethodSet(types.NewPointer(obj.Type()))

	g.Printf("public static final class %s implements go.Seq.Object {\n", obj.Name())
	g.Indent()
	g.Printf("private static final String DESCRIPTOR = \"go.%s.%s\";\n", g.pkg.Name(), obj.Name())
	for i, f := range fields {
	g.Printf("private static final int FIELD_%s_GET = 0x%x0f;\n", f.Name(), i)
	g.Printf("private static final int FIELD_%s_SET = 0x%x1f;\n", f.Name(), i)
	}
	for i, m := range methods {
	g.Printf("private static final int CALL_%s = 0x%x0c;\n", m.Name(), i)
	}
	g.Printf("\n")

	g.Printf("private go.Seq.Ref ref;\n\n")

	n := obj.Name()
	g.Printf("private %s(go.Seq.Ref ref) { this.ref = ref; }\n\n", n)
	g.Printf(`public go.Seq.Ref ref() { return ref; }

	public void call(int code, go.Seq in, go.Seq out) {
	throw new RuntimeException("internal error: cycle: cannot call concrete proxy");
	}

	`)

	for _, f := range fields {
	g.Printf("public %s get%s() {\n", g.javaType(f.Type()), f.Name())
	g.Indent()
	g.Printf("Seq in = new Seq();\n")
	g.Printf("Seq out = new Seq();\n")
	g.Printf("in.writeRef(ref);\n")
	g.Printf("Seq.send(DESCRIPTOR, FIELD_%s_GET, in, out);\n", f.Name())
	if seqType(f.Type()) == "Ref" {
	g.Printf("return new %s(out.read%s);\n", g.javaType(f.Type()), seqRead(f.Type()))
	} else {
	g.Printf("return out.read%s;\n", seqRead(f.Type()))
	}
	g.Outdent()
	g.Printf("}\n\n")

	g.Printf("public void set%s(%s v) {\n", f.Name(), g.javaType(f.Type()))
	g.Indent()
	g.Printf("Seq in = new Seq();\n")
	g.Printf("Seq out = new Seq();\n")
	g.Printf("in.writeRef(ref);\n")
	g.Printf("in.write%s;\n", seqWrite(f.Type(), "v"))
	g.Printf("Seq.send(DESCRIPTOR, FIELD_%s_SET, in, out);\n", f.Name())
	g.Outdent()
	g.Printf("}\n\n")
	}

	for _, m := range methods {
	g.genFunc(m, true)
	}

	g.Printf("@Override public boolean equals(Object o) {\n")
	g.Indent()
	g.Printf("if (o == null \|\| !(o instanceof %s)) {\n return false;\n}\n", n)
	g.Printf("%s that = (%s)o;\n", n, n)
	for _, f := range fields {
	nf := f.Name()
	g.Printf("%s this%s = get%s();\n", g.javaType(f.Type()), nf, nf)
	g.Printf("%s that%s = that.get%s();\n", g.javaType(f.Type()), nf, nf)
	if isJavaPrimitive(f.Type()) {
	g.Printf("if (this%s != that%s) {\n return false;\n}\n", nf, nf)
	} else {
	g.Printf("if (this%s == null) {\n", nf)
	g.Indent()
	g.Printf("if (that%s != null) {\n return false;\n}\n", nf)
	g.Outdent()
	g.Printf("} else if (!this%s.equals(that%s)) {\n return false;\n}\n", nf, nf)
	}
	}
	g.Printf("return true;\n")
	g.Outdent()
	g.Printf("}\n\n")

	g.Printf("@Override public int hashCode() {\n")
	g.Printf(" return java.util.Arrays.hashCode(new Object[] {")
	for i, f := range fields {
	if i > 0 {
	g.Printf(", ")
	}
	g.Printf("get%s()", f.Name())
	}
	g.Printf("});\n")
	g.Printf("}\n\n")

	// TODO(crawshaw): use String() string if it is defined.
	g.Printf("@Override public String toString() {\n")
	g.Indent()
	g.Printf("StringBuilder b = new StringBuilder();\n")
	g.Printf(`b.append("%s").append("{");`, obj.Name())
	g.Printf("\n")
	for _, f := range fields {
	n := f.Name()
	g.Printf(`b.append("%s:").append(get%s()).append(",");`, n, n)
	g.Printf("\n")
	}
	g.Printf(`return b.append("}").toString();`)
	g.Printf("\n")
	g.Outdent()
	g.Printf("}\n\n")

	g.Outdent()
	g.Printf("}\n\n")
	}

	func (g javaGen) genInterfaceStub(o types.TypeName, m *types.Interface) {
	g.Printf("public static abstract class Stub implements %s {\n", o.Name())
	g.Indent()

	g.Printf("static final String DESCRIPTOR = \"go.%s.%s\";\n\n", g.pkg.Name(), o.Name())
	g.Printf("private final go.Seq.Ref ref;\n")
	g.Printf("public Stub() {\n ref = go.Seq.createRef(this);\n}\n\n")
	g.Printf("public go.Seq.Ref ref() { return ref; }\n\n")

	g.Printf("public void call(int code, go.Seq in, go.Seq out) {\n")
	g.Indent()
	g.Printf("switch (code) {\n")

	for i := 0; i < m.NumMethods(); i++ {
	f := m.Method(i)
	g.Printf("case Proxy.CALL_%s: {\n", f.Name())
	g.Indent()

	sig := f.Type().(*types.Signature)
	params := sig.Params()
	for i := 0; i < params.Len(); i++ {
	p := sig.Params().At(i)
	jt := g.javaType(p.Type())
	g.Printf("%s param_%s;\n", jt, paramName(params, i))
	g.genRead("param_"+paramName(params, i), "in", p.Type())
	}

	res := sig.Results()
	var returnsError bool
	var numRes = res.Len()
	if (res.Len() == 1 && isErrorType(res.At(0).Type())) \|\|
	(res.Len() == 2 && isErrorType(res.At(1).Type())) {
	numRes -= 1
	returnsError = true
	}

	if returnsError {
	g.Printf("try {\n")
	g.Indent()
	}

	if numRes > 0 {
	g.Printf("%s result = ", g.javaType(res.At(0).Type()))
	}

	g.Printf("this.%s(", f.Name())
	for i := 0; i < params.Len(); i++ {
	if i > 0 {
	g.Printf(", ")
	}
	g.Printf("param_%s", paramName(params, i))
	}
	g.Printf(");\n")

	if numRes > 0 {
	g.Printf("out.write%s;\n", seqWrite(res.At(0).Type(), "result"))
	}
	if returnsError {
	g.Printf("out.writeString(null);\n")
	g.Outdent()
	g.Printf("} catch (Exception e) {\n")
	g.Indent()
	if numRes > 0 {
	resTyp := res.At(0).Type()
	g.Printf("%s result = %s;\n", g.javaType(resTyp), g.javaTypeDefault(resTyp))
	g.Printf("out.write%s;\n", seqWrite(resTyp, "result"))
	}
	g.Printf("out.writeString(e.getMessage());\n")
	g.Outdent()
	g.Printf("}\n")
	}
	g.Printf("return;\n")
	g.Outdent()
	g.Printf("}\n")
	}

	g.Printf("default:\n throw new RuntimeException(\"unknown code: \"+ code);\n")
	g.Printf("}\n")
	g.Outdent()
	g.Printf("}\n")

	g.Outdent()
	g.Printf("}\n\n")
	}

	const javaProxyPreamble = `static final class Proxy implements %s {
	static final String DESCRIPTOR = Stub.DESCRIPTOR;

	private go.Seq.Ref ref;

	Proxy(go.Seq.Ref ref) { this.ref = ref; }

	public go.Seq.Ref ref() { return ref; }

	public void call(int code, go.Seq in, go.Seq out) {
	throw new RuntimeException("cycle: cannot call proxy");
	}

	`

	func (g javaGen) genInterface(o types.TypeName) {
	iface := o.Type().(types.Named).Underlying().(types.Interface)

	g.Printf("public interface %s extends go.Seq.Object {\n", o.Name())
	g.Indent()

	methodSigErr := false
	for i := 0; i < iface.NumMethods(); i++ {
	if err := g.funcSignature(iface.Method(i), false); err != nil {
	methodSigErr = true
	g.errorf("%v", err)
	}
	g.Printf(";\n\n")
	}
	if methodSigErr {
	return // skip stub generation, more of the same errors
	}

	g.genInterfaceStub(o, iface)

	g.Printf(javaProxyPreamble, o.Name())
	g.Indent()

	for i := 0; i < iface.NumMethods(); i++ {
	g.genFunc(iface.Method(i), true)
	}
	for i := 0; i < iface.NumMethods(); i++ {
	g.Printf("static final int CALL_%s = 0x%x0a;\n", iface.Method(i).Name(), i+1)
	}

	g.Outdent()
	g.Printf("}\n")

	g.Outdent()
	g.Printf("}\n\n")
	}

	func isErrorType(T types.Type) bool {
	return T == types.Universe.Lookup("error").Type()
	}

	func isJavaPrimitive(T types.Type) bool {
	b, ok := T.(*types.Basic)
	if !ok {
	return false
	}
	switch b.Kind() {
	case types.Bool, types.Uint8, types.Float32, types.Float64,
	types.Int, types.Int8, types.Int16, types.Int32, types.Int64:
	return true
	}
	return false
	}

	// javaType returns a string that can be used as a Java type.
	func (g *javaGen) javaType(T types.Type) string {
	switch T := T.(type) {
	case *types.Basic:
	switch T.Kind() {
	case types.Bool:
	return "boolean"
	case types.Int:
	return "long"
	case types.Int8:
	return "byte"
	case types.Int16:
	return "short"
	case types.Int32:
	return "int"
	case types.Int64:
	return "long"
	case types.Uint8:
	// TODO(crawshaw): Java bytes are signed, so this is
	// questionable, but vital.
	return "byte"
	// TODO(crawshaw): case types.Uint, types.Uint16, types.Uint32, types.Uint64:
	case types.Float32:
	return "float"
	case types.Float64:
	return "double"
	case types.String:
	return "String"
	default:
	g.errorf("unsupported return type: %s", T)
	return "TODO"
	}
	case *types.Slice:
	elem := g.javaType(T.Elem())
	return elem + "[]"

	case *types.Pointer:
	if _, ok := T.Elem().(*types.Named); ok {
	return g.javaType(T.Elem())
	}
	panic(fmt.Sprintf("unsupporter pointer to type: %s", T))
	case *types.Named:
	n := T.Obj()
	if n.Pkg() != g.pkg {
	panic(fmt.Sprintf("type %s is in package %s, must be defined in package %s", n.Name(), n.Pkg().Name(), g.pkg.Name()))
	}
	// TODO(crawshaw): more checking here
	return n.Name()
	default:
	g.errorf("unsupported javaType: %#+v, %s\n", T, T)
	return "TODO"
	}
	}

	// javaTypeDefault returns a string that represents the default value of the mapped java type.
	// TODO(hyangah): Combine javaType and javaTypeDefault?
	func (g *javaGen) javaTypeDefault(T types.Type) string {
	switch T := T.(type) {
	case *types.Basic:
	switch T.Kind() {
	case types.Bool:
	return "false"
	case types.Int, types.Int8, types.Int16, types.Int32,
	types.Int64, types.Uint8, types.Float32, types.Float64:
	return "0"
	case types.String:
	return "null"
	default:
	g.errorf("unsupported return type: %s", T)
	return "TODO"
	}
	case types.Slice, types.Pointer, *types.Named:
	return "null"

	default:
	g.errorf("unsupported javaType: %#+v, %s\n", T, T)
	return "TODO"
	}
	}

	var paramRE = regexp.MustCompile(`^p[0-9]*$`)

	// paramName replaces incompatible name with a p0-pN name.
	// Missing names, or existing names of the form p[0-9] are incompatible.
	// TODO(crawshaw): Replace invalid unicode names.
	func paramName(params *types.Tuple, pos int) string {
	name := params.At(pos).Name()
	if name == "" \|\| name == "_" \|\| paramRE.MatchString(name) {
	name = fmt.Sprintf("p%d", pos)
	}
	return name
	}

	func (g javaGen) funcSignature(o types.Func, static bool) error {
	sig := o.Type().(*types.Signature)
	res := sig.Results()

	var returnsError bool
	var ret string
	switch res.Len() {
	case 2:
	if !isErrorType(res.At(1).Type()) {
	return fmt.Errorf("second result value must be of type error: %s", o)
	}
	returnsError = true
	ret = g.javaType(res.At(0).Type())
	case 1:
	if isErrorType(res.At(0).Type()) {
	returnsError = true
	ret = "void"
	} else {
	ret = g.javaType(res.At(0).Type())
	}
	case 0:
	ret = "void"
	default:
	return fmt.Errorf("too many result values: %s", o)
	}

	g.Printf("public ")
	if static {
	g.Printf("static ")
	}
	g.Printf("%s %s(", ret, o.Name())
	params := sig.Params()
	for i := 0; i < params.Len(); i++ {
	if i > 0 {
	g.Printf(", ")
	}
	v := sig.Params().At(i)
	name := paramName(params, i)
	jt := g.javaType(v.Type())
	g.Printf("%s %s", jt, name)
	}
	g.Printf(")")
	if returnsError {
	g.Printf(" throws Exception")
	}
	return nil
	}

	func (g javaGen) genFunc(o types.Func, method bool) {
	if err := g.funcSignature(o, !method); err != nil {
	g.errorf("%v", err)
	return
	}
	sig := o.Type().(*types.Signature)
	res := sig.Results()

	g.Printf(" {\n")
	g.Indent()
	g.Printf("go.Seq _in = new go.Seq();\n")
	g.Printf("go.Seq _out = new go.Seq();\n")

	returnsError := false
	var resultType types.Type
	if res.Len() > 0 {
	if !isErrorType(res.At(0).Type()) {
	resultType = res.At(0).Type()
	}
	if res.Len() > 1 \|\| isErrorType(res.At(0).Type()) {
	returnsError = true
	}
	}
	if resultType != nil {
	t := g.javaType(resultType)
	g.Printf("%s _result;\n", t)
	}

	if method {
	g.Printf("_in.writeRef(ref);\n")
	}
	params := sig.Params()
	for i := 0; i < params.Len(); i++ {
	p := params.At(i)
	g.Printf("_in.write%s;\n", seqWrite(p.Type(), paramName(params, i)))
	}
	g.Printf("Seq.send(DESCRIPTOR, CALL_%s, _in, _out);\n", o.Name())
	if resultType != nil {
	g.genRead("_result", "_out", resultType)
	}
	if returnsError {
	g.Printf(`String _err = _out.readString();
	if (_err != null) {
	throw new Exception(_err);
	}
	`)
	}
	if resultType != nil {
	g.Printf("return _result;\n")
	}
	g.Outdent()
	g.Printf("}\n\n")
	}

	func (g *javaGen) genRead(resName, seqName string, T types.Type) {
	switch T := T.(type) {
	case *types.Pointer:
	// TODO(crawshaw): test *int
	// TODO(crawshaw): test **Generator
	switch T := T.Elem().(type) {
	case *types.Named:
	o := T.Obj()
	if o.Pkg() != g.pkg {
	g.errorf("type %s not defined in package %s", T, g.pkg)
	return
	}
	g.Printf("%s = new %s(%s.readRef());\n", resName, o.Name(), seqName)
	default:
	g.errorf("unsupported type %s", T)
	}
	case *types.Named:
	switch T.Underlying().(type) {
	case types.Interface, types.Pointer:
	o := T.Obj()
	if o.Pkg() != g.pkg {
	g.errorf("type %s not defined in package %s", T, g.pkg)
	return
	}
	g.Printf("%s = new %s.Proxy(%s.readRef());\n", resName, o.Name(), seqName)
	default:
	g.errorf("unsupported, direct named type %s", T)
	}
	default:
	g.Printf("%s = %s.read%s();\n", resName, seqName, seqType(T))
	}
	}

	func (g *javaGen) errorf(format string, args ...interface{}) {
	g.err = append(g.err, fmt.Errorf(format, args...))
	}

	const javaPreamble = `// Java Package %s is a proxy for talking to a Go program.
	// gobind -lang=java %s
	//
	// File is generated by gobind. Do not edit.
	package go.%s;

	import go.Seq;

	`

	func (g *javaGen) gen() error {
	g.Printf(javaPreamble, g.pkg.Name(), g.pkg.Path(), g.pkg.Name())

	firstRune, size := utf8.DecodeRuneInString(g.pkg.Name())
	className := string(unicode.ToUpper(firstRune)) + g.pkg.Name()[size:]

	g.Printf("public abstract class %s {\n", className)
	g.Indent()
	g.Printf("private %s() {} // uninstantiable\n\n", className)
	scope := g.pkg.Scope()
	names := scope.Names()
	var funcs []string
	for _, name := range names {
	obj := scope.Lookup(name)
	if !obj.Exported() {
	continue
	}

	switch o := obj.(type) {
	// TODO(crawshaw): case *types.Const:
	// TODO(crawshaw): case *types.Var:
	case *types.Func:
	g.genFunc(o, false)
	funcs = append(funcs, o.Name())
	case *types.TypeName:
	named := o.Type().(*types.Named)
	switch t := named.Underlying().(type) {
	case *types.Struct:
	g.genStruct(o, t)
	case *types.Interface:
	g.genInterface(o)
	default:
	g.errorf("%s: cannot generate binding for %s: %T", g.fset.Position(o.Pos()), o.Name(), t)
	continue
	}
	default:
	g.errorf("unsupported exported type: ", obj)
	}
	}

	for i, name := range funcs {
	g.Printf("private static final int CALL_%s = %d;\n", name, i+1)
	}

	g.Printf("private static final String DESCRIPTOR = %q;\n", g.pkg.Name())
	g.Outdent()
	g.Printf("}\n")

	if len(g.err) > 0 {
	return g.err
	}
	return nil
	}