java构造函数：this（。）

为什么输出为“021”？ 为什么有“0”和“1”（因为“我”得到“2”为什么它变成“1”）？

public class C { protected int i; public C(int i){ this(i,i); System.out.print(this.i); this.i=i; } public C(int i, int j) { System.out.print(this.i); this.i=i+j; } public C(){ this(1); System.out.print(i); } public static void main(String[] args) { C c=new C(); }} 

Answer 1

C()调用C(1)调用C(1,1)

• C(1,1)打印0 （ this.i的默认值）并为this.i分配2（ i+j ）
• 然后C(1)打印2并将1分配给this.i
• 然后C()打印1

Answer 2

我认为这对理解更好：

 public C(int i) { this(i, i); System.out.println("*"+this.i); this.i = i; } public C(int i, int j) { System.out.println("@"+this.i); this.i = i + j; } public C() { this(1); System.out.println("#"+i); } 

现在，您可以在调用C（）时获取这些方法的序列;

Answer 3

在这里代码评论，你现在就能理解你的问题，

 public class C { protected int i; public C(int i) { this(i, i); // got to two parameter constructer and after the result print the next line System.out.print(" + second "+this.i); // print value of i which is come from C(int i, int j) = 2 this.i = i; // set the value of i to 1 } public C(int i, int j) { System.out.print("first "+this.i); // print the value of i (in this case 0 the default value) this.i = i + j; // set i to 2 } public C() { this(1); // got to one parameter constructer and after the result print the next line System.out.print(" + Third is "+i); // print value of i which is come from C(int i) = 1 } public static void main(String[] args) { C c = new C(); } } 

我希望有所帮助。