延迟加载一个对象
2017-01-21 20:39:14
阅读1662次
使用对象的前才去实例化对象，这叫延迟加载对象(LazyLoad)。在懒汉单例模式中有用到。代码如下：
class Simple{
private String s;
public Simple(String s){
this.s = s;
}
public String toString(){
return s;
}
public void setString(String s){
this.s = s;
}
}class Second{
private Simple simple;
private String s;
public Second(String s){
this.s = s;
}
public void check(){
if(simple == null){
System.out.println("not init the simple object");
}else{
System.out.println("init the simple object");
}
}
private Simple lazy(){
if(simple == null){
simple = new Simple(s);
return simple;
}
return simple;
}
public Simple getSimple(){
return lazy();
}
public void setSimple(String s){
lazy().setString(s);
}
public String toString(){
return lazy().toString();
}
}public class Test1 {
public static void main(String[] args) {
Second second = new Second("Init String");
//此时并没有实例化Simple对象
second.check();
// 需要Simple时候才去实例化
System.out.println(second.getSimple());
second.check();
System.out.println(second); // toString() call
second.setSimple("New String");
System.out.println(second);
}
}输出：
not init the simple object Init String init the simple object Init String New String
参考《Java编程思想》P126
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