Java中的==和equals

public static void abc() { 
    String abc = null; 
    try { 
        if (abc.equals(null)) 
            System.out.println("1"); 
        abc = "abc"; 
        if (abc == "abc") 
            System.out.println("2"); 
    } catch (Exception e) { 
        System.out.println("3"); 
    } finally { 
        System.out.println("4"); 
    } 
    System.out.println("5"); 
} 

结果：

3

4

5

在第4行的时候报了java.lang.NullPointerException异常

如果是下面这样

public static void abc() { 
    String abc = null; 
    try { 
        if (abc.equals(null)) 
            System.out.println("1"); 
    } catch (Exception e) { 
        e.printStackTrace(); 
        abc = "abc"; 
        if (abc == "abc") 
            System.out.println("2"); 
        System.out.println("3"); 
    } finally { 
        System.out.println("4"); 
    } 
    System.out.println("5"); 
} 

结果

2

3

4

5

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