AST[Abstract Syntax Tree]

Abstract Syntax Tree

AST abstract syntax tree （抽象语法结构树），是对java语言的一种抽象，每个节点都能对应到一种java语法，最终一个java文件就是由一棵节点树构成。
package com.sun.tools.javac.tree;

AST 节点类型

com.sun.source.tree.Tree.Kind

枚举类型	Tree节点类型	定义	示例
ANNOTATED_TYPE	AnnotatedTypeTree	注解类型，可以用在任何类型上 注解的Target为：TYPE_PARAMETER TYPE_USE	@NotNull String
ANNOTATION	AnnotationTree	普通的注解	@Data @JsonProperties(value="sdf")
TYPE_ANNOTATION	AnnotationTree
ARRAY_ACCESS	ArrayAccessTree	数组访问	array[3]
ARRAY_TYPE	ArrayTypeTree	数组类型	int[]
ASSIGNMENT	AssignmentTree	赋值	a = 1
BLOCK	BlockTree	语句块	{} { statements } static
BREAK	BreakTree	break	break; break label;
CASE	CaseTree	case 语句	case expression：statements default: statements
CATCH	CatchTree	catch 语句	catch(parameter) block 注：这些语句会有嵌套问题
CLASS INTERFACE ENUM ANNOTATION_TYPE	ClassTree	class 定义	modifiers class simpleName typeParameters extends extendsClause implements implementsClause { members }
COMPILATION_UNIT	CompilationUnitTree	一个编译单元 包括源文件和package-info.java
CONDITIONAL_EXPRESSION	ConditionalExpressionTree	三元运算符	a == 1 ? 1 : 0
CONTINUE	ContinueTree	continue 语句	continue; continue label;
DO_WHILE_LOOP	DoWhileLoopTree	do...while
ENHANCED_FOR_LOOP	EnhancedForLoopTree	增强for	for(int i: intlist)
EXPRESSION_STATEMENT	ExpressionStatementTree	语句
MEMBER_SELECT	MemberSelectTree	对象.操作	aClass.aparams
MEMBER_REFERENCE	MemberReferenceTree	成员引用表达式
FOR_LOOP	ForLoopTree	for循环
IDENTIFIER	IdentifierTree	识别符，与literal区分开	a = 1 a 就是一个identifier
IF	IfTree
IMPORT	ImportTree
INSTANCE_OF	InstanceOfTree	instanceof 表达式
LABELED_STATEMENT	LabeledStatementTree	label语法	label : statement
METHOD	MethodTree	方法定义	方法 modifiers typeParameters type name (parameters ) body 注解 modifiers type name () default defaultValue
METHOD_INVOCATION	MethodInvocationTree	method invoke语法
MODIFIERS	ModifiersTree	修饰符（Modifier） 包括注解
NEW_ARRAY	NewArrayTree
NEW_CLASS	NewClassTree
LAMBDA_EXPRESSION	LambdaExpressionTree	lambda表达式
PRIMITIVE_TYPE	PrimitiveTypeTree	基础类型
RETURN	ReturnTree	return
EMPTY_STATEMENT	EmptyStatementTree	空的";"
SWITCH	SwitchTree
SYNCHRONIZED	SynchronizedTree
THROW	ThrowTree
TRY	TryTree
PARAMETERIZED_TYPE	ParameterizedTypeTree	泛型	List
UNION_TYPE	UnionTypeTree	多变量声明	try { }catch(Exception e1
INTERSECTION_TYPE	IntersectionTypeTree		T extends MyA & MyB
TYPE_CAST	TypeCastTree	强转语句	(int)a
TYPE_PARAMETER	TypeParameterTree
VARIABLE	VariableTree	变量	modifiers type name initializer ; modifiers type qualified-name.this
WHILE_LOOP	WhileLoopTree
POSTFIX_INCREMENT POSTFIX_DECREMENT PREFIX_INCREMENT PREFIX_DECREMENT UNARY_PLUS UNARY_MINUS BITWISE_COMPLEMENT LOGICAL_COMPLEMENT	UnaryTree	运算符	++、--、+、-、~、！、*、/、%
MULTIPLY DIVIDE REMAINDER PLUS MINUS LEFT_SHIFT RIGHT_SHIFT UNSIGNED_RIGHT_SHIFT LESS_THAN GREATER_THAN LESS_THAN_EQUAL GREATER_THAN_EQUAL EQUAL_TO NOT_EQUAL_TO AND XOR OR CONDITIONAL_AND CONDITIONAL_OR	BinaryTree	两元运算
MULTIPLY_ASSIGNMENT DIVIDE_ASSIGNMENT REMAINDER_ASSIGNMENT PLUS_ASSIGNMENT MINUS_ASSIGNMENT LEFT_SHIFT_ASSIGNMENT RIGHT_SHIFT_ASSIGNMENT UNSIGNED_RIGHT_SHIFT_ASSIGNMENT AND_ASSIGNMENT XOR_ASSIGNMENT OR_ASSIGNMENT	CompoundAssignmentTree	赋值运算符	+=、-=、*=
INT_LITERAL LONG_LITERAL FLOAT_LITERAL DOUBLE_LITERAL BOOLEAN_LITERAL CHAR_LITERAL STRING_LITERAL NULL_LITERAL	LiteralTree	字面值	a = 1 (1就是)
OTHER	null

JCTree

com.sun.tools.javac.tree.JCTree 是Tree的一个抽象实现类，有各种实现类，代表着一个个的AST节点。
实现类都是JCTree的内部类 ;

JCTree.Factory

JCTree的各种JC类的构造函数都是protected，也就是说，并不能直接进行初始化，所以现在要使用Factory，Factory是各种JC类的工厂定义。

com.sun.tools.javac.tree.TreeMaker

TreeMaker是JCTree.Factory实现 ;它是常使用的一个类 ;
所有语法节点都是由它生成的，根据Name对象构建一个语法节点。

断点观察

JCTree.JCMethodDecl

   public static class JCMethodDecl extends JCTree implements MethodTree {
        public JCModifiers mods; //方法修饰符 
        public Name name; //方法名称
        public JCExpression restype;//方法返回值类型
        public List<JCTypeParameter> typarams; //方法入参
        public JCVariableDecl recvparam; //方法变量
        public List<JCVariableDecl> params; //方法变量列表
        public List<JCExpression> thrown; //异常
        public JCBlock body; //方法体
        public JCExpression defaultValue; //默认值
        public Symbol.MethodSymbol sym; //所属类

JCModifiers

    public static class JCModifiers extends JCTree implements ModifiersTree {
        public long flags;
        public List<JCAnnotation> annotations;

com.sun.tools.javac.code.Flags

public class Flags {
    public static final int PUBLIC = 1;
    public static final int PRIVATE = 2;
    public static final int PROTECTED = 4;
    public static final int STATIC = 8;
    public static final int FINAL = 16;
    public static final int SYNCHRONIZED = 32;
    public static final int VOLATILE = 64;
    public static final int TRANSIENT = 128;
    public static final int NATIVE = 256;
    public static final int INTERFACE = 512;
    public static final int ABSTRACT = 1024;
     ...
    public static final int ACC_SUPER = 32;
    public static final int ACC_BRIDGE = 64;

com.sun.tools.javac.util.Name

com.sun.tools.javac.util.SharedNameTable.NameImpl extends Name

com.sun.tools.javac.tree.JCTree.JCExpression

com.sun.tools.javac.tree.JCTree.JCPrimitiveTypeTree extends JCExpression

treeMaker.pos = jcMethodDecl.pos; 的作用

pos属性代表AST节点在源代码中的位置。通过将treeMaker对象的pos属性设置为jcMethodDecl对象的位置，新创建的AST节点将与源代码中的原始方法声明具有相同的位置 ,这在调试方面非常重要。