public class Test {
    public static void main(String[] args) {
        String x = "1";
        int y = 2;
        int z = 3;
        System.out.println(x+y+z);
    }
}

當String物件進行"+"操作，編譯時會將String類變為StringBuilder進行append( )處理，而append( )方法的功能就是字串拼接。且優先順序相同從左到右計算。

public class Test {
    public
 
 static void main(String[] args) {
        String x = "1";
        int y = 2;
        int z = 3;
        //System.out.println(x+y+z);
        StringBuilder sb = new StringBuilder();
        System.out.println(sb.append(x).append(y).append(z));
    }
}