[原]toString()方法的复写作用, 以及打印集合.

Object o = new Object();
System.out.println(o); //结果java.lang.Object@bab5e85

public static class Person { // 自定义Person类, 未重写 toString()函数
    Integer id = 1;
    String name = "duenboa";

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

Person  p = new Person();
System.out.println(p); //com.hoss.weixin.controller.eflow.EfHrChgController$Person@2e7aacc1

public static class Person {
    Integer id = 1;
    String name = "duenboa";

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name=‘" + name + ‘\‘‘ +
                ‘}‘;
    }

Person  p = new Person();
System.out.println(p); //Person{id=1, name=‘duenboa‘}

System.out.println(map);

 这句最基本的标准打印控制函数的实现又是如何调用的呢?

在java.io.PrintStream.java类源码中, 依旧还是通过String.valueOf(Obj)去获取String.

public void println(Object x) {
    String s = String.valueOf(x);  //1
    synchronized (this) {
        print(s);
        newLine();
    }
}

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
}

List list = new ArrayList();
list.add(new Person());
list.add(new Person());
System.out.println(list); // Person类有重写toString方法时[Person{id=1, name=‘李克用‘}, Person{id=1, name=‘李克用‘}]
System.out.println(list); // Person类未重写toString方法时[com.hoss.weixin.controller.eflow.EfHrChgController$Person@53ffb7d4, com.hoss.weixin.controller.eflow.EfHrChgController$Person@397dea61]


Map<Integer, Person> map = Maps.newHashMap();
map.put(1,new Person());
map.put(2,new Person());
System.out.println(map);//{1=Person{id=1, name=‘李克用‘}, 2=Person{id=1, name=‘李克用‘}}
System.out.println(map);//{1=com.hoss.weixin.controller.eflow.EfHrChgController$Person@70d4c191, 2=com.hoss.weixin.controller.eflow.EfHrChgController$Person@1ff05076}