preincrement / postincrement in java
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Can someome help me to understand why: 

    int i=1;
    int j=1;
    int k=1;
    int l=1;
    		
    System.out.println(i++ + i++);	
    System.out.println(++j + ++j);  
    System.out.println(k++ + ++k);  
    System.out.println(++l + l++);

give:

3  
5  
4  
4  