java 入门测试代码(四)

java 数组和容器的简单使用：

       // 数组的使用
        int [] array = {1,2,3,4};
        System.out.println( array );
        System.out.format( "index 2:%d\n",array[2] );

        // list 使用
        List<Integer> list = new ArrayList<Integer>();

        list.add( 10 );
        list.add( 11 );
        list.add( 12 );

        // 遍历
        for(Integer data: list) {
            System.out.println( "list:" + data );
        }


        // hash map 使用
        Map< String, Integer > m = new HashMap< String, Integer >();

        m.put( "zhangsan", 19 );
        m.put( "lisi", 49 );
        m.put( "wangwu", 19 );
        m.put( "lisi", 20 );
        m.put( "hanmeimei", 0 );

        // 遍历
        Iterator it = m.keySet().iterator();
        while( it.hasNext() )
        {
            String key;
            int value;
            key = it.next().toString();
            value = m.get(key);

            System.out.println( key+"--" + value );
        }


        // set 使用
        Set<Integer> inset = new HashSet<Integer>();
        inset.add(2);
        inset.add(2);
        inset.add(3);

        Iterator iterator = inset.iterator();
        while (iterator.hasNext())
        {
            System.out.println( "inset:"+iterator.next() );
        }

根据字段进行排序：

    // 根据字段排序
    static void test7()
    {
        class CPerson {
            int index;
            String name;
            int age;
        }
        
        List<CPerson> people = new ArrayList<CPerson>();

        CPerson p1 = new CPerson();
        p1.age = 6;
        p1.name = "nick";
        p1.index = 0;

        CPerson p2 = new CPerson();
        p2.index = 1;
        p2.age = 12;
        p2.name = "jhon";

        CPerson p3 = new CPerson();
        p3.index = 2;
        p3.age = 3;
        p3.name = "amy";

        people.add(p1);
        people.add(p2);
        people.add(p3);

        // 用 lambda 排序
        people.sort((h1, h2) -> h1.age - h2.age);
        //people.sort((h1, h2) -> h2.age - h1.age);
        /* 
        // 从小到大
        Collections.sort(people, new Comparator<CPerson>() {
            public int compare(CPerson u1, CPerson u2) {
                if (u1.age > u2.age) {
                    return 1;
                }
                if (u1.age == u2.age) {
                    return 0;
                }
                return -1;
            }
        });
        
         // 从大到小的顺序
        Collections.sort(people, new Comparator<CPerson>() {
            public int compare(CPerson u1, CPerson u2) {
                if (u1.age > u2.age) {
                    return -1;
                }
                if (u1.age == u2.age) {
                    return 0;
                }
                return 1;
            }
        });
         */

        for (CPerson u : people) {
            System.out.format( "index:%d age:%d name%s", u.index, u.age, u.name );
        }
    }