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String s = null;
s += "abc";
System.out.println(s);
package syn;
//不能改动此Test类
public class Test extends Thread{
private TestDo testDo;
private String key;
private String value;
public Test(String key,String key2,String value){
this.testDo = TestDo.getInstance();
/*常量"1"和"1"是同一个对象,下面这行代码就是要用"1"+""的方式产生新的对象,
以实现内容没有改变,仍然相等(都还为"1"),但对象却不再是同一个的效果*/
this.key = key+key2;
this.value = value;
}
public static void main(String[] args) throws InterruptedException{
Test a = new Test("1","","1");
Test b = new Test("1","","2");
Test c = new Test("3","","3");
Test d = new Test("4","","4");
System.out.println("begin:"+(System.currentTimeMillis()/1000));
a.start();
b.start();
c.start();
d.start();
}
public void run(){
testDo.doSome(key, value);
}
}
class TestDo {
private TestDo() {}
private static TestDo _instance = new TestDo();
public static TestDo getInstance() {
return _instance;
}
public void doSome(Object key, String value) {
// 以大括号内的是需要局部同步的代码,不能改动!
{
try {
Thread.sleep(1000);
System.out.println(key+":"+value + ":"
+ (System.currentTimeMillis() / 1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
String a = "a" + "b";
String b = "a" + "b";
System.out.println(a == b);
String a = "a";
String b = "b";
String s1 = a + b;
String s2 = a + b;
System.out.println(s1 == s2);
package test;
public class T {
public static void main(String[] args) {
String a1 = "1";
String b1 = "";
String s1 = a1 + b1;
String s2 = a1 + b1;
System.out.println(s1 == s2);
}
}
Compiled from "T.java"
public class test.T extends java.lang.Object{
public test.T();
Code:
0: aload_0
1: invokespecial #8; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: ldc #16; //String 1
2: astore_1
3: ldc #18; //String
5: astore_2
6: new #20; //class java/lang/StringBuilder
9: dup
10: aload_1
11: invokestatic #22; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
14: invokespecial #28; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
17: aload_2
18: invokevirtual #31; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
21: invokevirtual #35; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
24: astore_3
25: new #20; //class java/lang/StringBuilder
28: dup
29: aload_1
30: invokestatic #22; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
33: invokespecial #28; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
36: aload_2
37: invokevirtual #31; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
40: invokevirtual #35; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
43: astore 4
45: getstatic #39; //Field java/lang/System.out:Ljava/io/PrintStream;
48: aload_3
49: aload 4
51: if_acmpne 58
54: iconst_1
55: goto 59
58: iconst_0
59: invokevirtual #45; //Method java/io/PrintStream.println:(Z)V
62: return
}
22: ldc #74; //String 1
24: astore_1
25: ldc #76; //String
27: astore_2
28: new #78; //class java/lang/StringBuilder
31: dup
32: aload_1
33: invokestatic #80; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
36: invokespecial #84; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
39: aload_2
40: invokevirtual #85; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
43: invokevirtual #89; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
46: astore_3
47: new #78; //class java/lang/StringBuilder
50: dup
51: aload_1
52: invokestatic #80; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
55: invokespecial #84; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
58: aload_2
59: invokevirtual #85; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
62: invokevirtual #89; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
public class Test {
public static void main(String[] args) {
String a1 = "1";
String b1 = "";
String s1 = a1 + b1;
String s2 = a1 + b1;
}
}