读完部分effective java 自己写的类Entity
自己写的Entity类，有四个属性，int，char，Sting，double，用了构造器方法，可以四个参数都有，也可以之后几个，但int是必须的。类还实现了comparable接口，重写了compareTo，equals，hashCode三个方法，这是我能想到的比较OK的类。
compareTo的比较方法是按int>char>String>double的顺序
equals方法中规中矩，比较而已
hashCode用的书中的方法,待思考
package com.util;public class Entity implements Comparable{private final int i;private final char c;private final String s;private final double d;public static class Builder {private final int i;private char c;private String s;private double d;public Builder(int i) {this.i = i;}public Builder setC(char c) {this.c = c;return this;}public Builder setS(String s) {this.s = s;return this;}public Builder setD(double d) {this.d = d;return this;}public Entity build() {return new Entity(this);}}private Entity(Builder b) {this.c = b.c;this.d = b.d;this.s = b.s;this.i = b.i;}@Overridepublic int compareTo(Object o) {if(this == o) return 0;if(!(o instanceof Entity))throw new IllegalArgumentException("Cannot compare Pair with " + o.getClass().getName());Entity e = (Entity)o;if(i == e.i) {if(c == e.c) {if((s == null && e.s == null) || (s != null && s.compareTo(e.s) == 0)) {if(Double.compare(d, e.d) == 0) {return 0;} else {return Double.compare(d, e.d);}} else {if( s == null && e.s != null) return -1;else if( e.s == null && s != null) return 1;else return s.compareTo(e.s);}} else {return c - e.c > 0 ? 1 : -1;}} else {return i - e.i > 0 ? 1 : -1;}}@Overridepublic boolean equals(Object obj) {if(!(obj instanceof Entity)) return false;Entity e = (Entity)obj;if(this.i == e.i)if(this.c == e.c) if( (s == null && e.s == null) || this.s.equals(e.s))if(this.d == e.d) return true;return false;}@Overridepublic String toString() {return "[int = " + i + ",char = " + c + ",String = " + s + ", double = " + d + "]";}@Overridepublic int hashCode() {int result = 17;result = 31*result + this.i;result = 31*result + (int)this.c;result = 31*result + (int)Math.round(d);result = 31*result + (int)s.charAt(0);return result ;}}package com.util;import junit.framework.Assert;import org.junit.Test;public class TestEntity {@Testpublic void testEquals() {Entity e1 = new Entity.Builder(3).setC('b').build();Entity e2 = new Entity.Builder(3).setC('b').build();Entity e3 = new Entity.Builder(3).build();Integer i = Integer.valueOf("3");Assert.assertEquals(e1.equals(e2), true);Assert.assertEquals(e1.equals(e3), false);Assert.assertEquals(e3.equals(i), false);}@Testpublic void testCompareTo() {Entity e1 = new Entity.Builder(3).setC('b').build();Entity e2 = new Entity.Builder(3).setC('b').build();Entity e3 = new Entity.Builder(3).setC('a').build();Entity e4 = new Entity.Builder(3).setC('b').setS("asd").build();Assert.assertEquals(e1.compareTo(e1), 0);Assert.assertEquals(e1.compareTo(e2), 0);Assert.assertEquals(e1.compareTo(e3), 1);Assert.assertEquals(e1.compareTo(e4), -1);}@Test(expected=IllegalArgumentException.class)public void testCompareTo2() {Entity e1 = new Entity.Builder(3).setC('b').build();Integer i = Integer.valueOf("3");Assert.assertEquals(e1.compareTo(i), 0);}}