String 不变性以及 Java 值传递和引用传递

String 不变性以及 Java 值传递和引用传递

public class Example {
	String str = new String("good");
	char[] ch = { 'a', 'b', 'c' };

	public static void main(String args[]) {
		Example ex = new Example();
		ex.change(ex.str, ex.ch);
		System.out.print(ex.str + " and ");
		System.out.print(ex.ch);
	}

	public void change(String str, char ch[]) {
		str = "test ok";
		ch[0] = 'g';
	}
}

点击查看结果

```
good and gbc
```

public class TestStringFinal {
	public static void main(String[] args) {
		String a = "hello";
		change(a);
		System.out.println(a);
	}

	public static void change(String name) {
		name = "world";
	}
}

点击查看结果

```
hello
```

public class Test {
	public static void main(String[] args){
		Test test = new Test();
		int a = 1;
		test.addInt(a);
		System.out.println(a);
		String str = "hello";
		test.addString(str);
		System.out.println(str);
		StringBuilder sb = new StringBuilder("hello");
		test.addBuilder(sb);
		System.out.println(sb.toString());
		Long m = 1L;
		Long n = 1L;
		System.out.println(m==n);
		m = 200L;
		n = 200L;
		System.out.println(m==n);
		String x = new String("hello");
		String y = "hello";
		System.out.println(x.equals(y));
		System.out.println(x == y);
	} 

	public void addInt(int a){
		a = a + 1;
	}

	public void addString(String str){
		str = str + "world";
	}

	public void addBuilder(StringBuilder sb){
		sb.append("world");
	}
}

点击查看结果

```
1
hello
helloworld
true
false
true
false
```

public class Test {
    // swap() doesn't swap i and j
    public static void swap(Integer i, Integer j) {
        Integer temp = new Integer(i);
        i = j;
        j = temp;
    }
    public static void main(String[] args) {
        Integer i = new Integer(10);
        Integer j = new Integer(20);
        swap(i, j);
        System.out.println("i = " + i + ", j = " + j);
    }
}

点击查看结果

```
i = 10, j = 20
```