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Javac (JC) Cookbook - How to introduce new attribute into exist class

發表於 2020-09-02 更新於 2020-09-03

Question

對已經存在的類別加入新的attribute

Answer

作法是透過TreeMaker#VerDef()來產生新的variable的定義，然後透過JCClassDecl的defs#prepend()加到類別的Class Tree上。

以下是使用TreeMaker#VerDef()產生serialVersionUID的定義和初始化。

private JCTree.JCVariableDecl genSerialVersionUIDVariable() {
    JCTree.JCModifiers modifiers = treeMaker.Modifiers(PRIVATE + STATIC + FINAL);
    Name id = names.fromString("serialVersionUID");
    JCTree.JCExpression varType = treeMaker.Type(new Type.JCPrimitiveType(TypeTag.LONG, null));
    JCTree.JCExpression init = treeMaker.Literal(1L);
    return treeMaker.VarDef(modifiers, id, varType, init);
}

以下是把VariableTree加到ClassTree的寫法

1	jcClassDecl.defs = jcClassDecl.defs.prepend(genSerialVersionUIDVariable());

這個VariableTree對應的java程式碼如下

1	private static final long serialVersionUID = 1L;

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