首先声明变量，然后赋值。该类与此相同：
class Foo { int a; int b; int c = b; int var1; int var2; public Foo() { a = b; var1 = var2; var2 = var1; }}您无法执行此
int a = b;操作的原因
b是，在创建对象时尚未定义，但是对象本身（即
this）及其所有成员变量都存在。
这是每个的说明：
int a = b; // Error: b has not been defined yet int a = this.b; // No error: 'this' has been defined ('this' is always defined in a class) int b; int c = b; // No error: b has been defined on the line before
