加错答案

Question

public class Container {
    private int value;
    public Container(int value){
        this.value=value;
    }
    public int getValue(){
        return this.value;
    }
    public int sum(Container c){
        return this.value+c.getValue();
    }
    public void main(){
        Container c1=new Container(1);
        Container c2=new Container(2);
        System.out.println("sum: " + c1.getValue()+c2.getValue());
        System.out.println("sum: " + c1.sum(c2));
    }
}

当我运行此代码时，我得到以下结果：

public class Container {
    private int value;
    public Container(int value){
        this.value=value;
    }
    public int getValue(){
        return this.value;
    }
    public int sum(Container c){
        return this.value+c.getValue();
    }
    public void main(){
        Container c1=new Container(1);
        Container c2=new Container(2);
        System.out.println("sum: " + c1.getValue()+c2.getValue());
        System.out.println("sum: " + c1.sum(c2));
    }
}

预期是：

sum: 12
sum: 3

有谁知道我为什么得到这些结果？

Answer 1

当您将+运算符与a一起使用时String，它将其视为连接，而不是加法，并且Java从左到右评估操作，因此"sum: " + c1.getValue()+c2.getValue()被评估为

"sum: " + 1 + 2
"sum: 1" + 2
"sum: 12"

如果要先使整数加法，则需要添加括号：

System.out.println("sum: " + (c1.getValue() + c2.getValue()));