java 值传递

package cn.test;
class G{
    int a;
    int b;
    public G(int a,int b) {
        this.a=a;
        this.b=b;
    }
    public int getA() {
        return a;
    }
    public void setA(int a) {
        this.a = a;
    }
    public int getB() {
        return b;
    }
    public void setB(int b) {
        this.b = b;
    }
    @Override
    public String toString() {
        return "G [a=" + a + ", b=" + b + "]";
    }
}
public class TestXinCan {
    public static void main(String[] args) {
        G g1=new G(1,1);
        System.out.println(g1);
        change(g1);
        System.out.println(g1);
    }
    public static void change(G g) {
        G g2=new G(2,2);　　//①
        /*g.setA(2);　　//②
        g.setB(2);*/
        g=g2;
    }
}

第一种方式 g1值不变，第二种方式g1值变了。